Many automotive vehicles are equipped with a fuse junction box which serves to hold a plurality of fuses associated with the various electrically powered devices of the vehicle. One widely used type of automotive fuse takes the form of a pair of parallel blade-type contacts with the fusable portion constituting a bridge between the two blades. The fusable link is encased in a transparent insulative plastic and may be color coded according to the ampere rating of the fuse. A representative fuse junction box comprises a plurality of fuse receptacles containing spring clip contacts which engage the blades when the buses are pushed blade-end first into the receptacles. When properly inserted, each fuse forms part of an electrical circuit and protects the circuit from over-current conditions.
Some circuits supplying power to vehicle electrical devices are configured such that they may be energized only if the vehicle ignition switch has been moved to the ON/RUN or ACC (accessory) positions. Typically this switch movement energizes a relay to close a contact and supply power to the circuit from the vehicle battery or generator. This ignition switch controlled circuit commonly known as the accessory circuit typically powers devices such as the radio power windows and electric window defroster. Since the ignition key is required to move the ignition switch to the ON/RUN or ACC positions devices powered by the accessory circuit cannot be left on inadvertently when the vehicle is parked and the ignition key is removed thus lessening the likelihood of the vehicle battery losing its charge.
Many other vehicle electrical devices are powered by circuits wired so that they may be supplied with power regardless of the ignition switch position. Devices such as the clock emergency flashers headlights and interior lights are included in what is known as the battery circuit being wired directly to the vehicle battery without passing through the ignition switch actuated relay.
It is known in the automotive industry to provide a fuse box wired to permit a particular electrical device to be switched between the two power supply configurations described above simply by moving the fuse protecting that device from first fuse receptacle to a second fuse receptacle. To achieve this one of the two fuse receptacles is wired to connect the electrical device to the accessory circuit and the other receptacle is wired to connect the device to the battery circuit. In effect the fuse for the device serves as a switch and the selection between the two power supply configurations may be made at the vehicle production plant, at the vehicle retail dealer, or by the vehicle owner/operator.
A drawback to this switchable circuit arrangement is that it is possible for a person unaware of the nature and function of the fuse switchable circuit described above to insert fuses into both of the commonly wired fuse receptacles simultaneously. This results in a short circuit condition which may cause any number of electrical devices to malfunction and/or may allow the vehicle battery to be drained of its charge.